This invention relates to shoring systems used to support the walls of open excavations. The shoring system comprises large shoring panels and rail posts. The rail post consists of at least two members, an outer member and an inner member. Both members of the rail post have laterally, on either side, panel guides allowing shoring panels to slide vertically within. In addition, the outer member has lengthwise a frontal guide interlocking the back guide provided to the inner member so that each member slides relatively to the other. The shoring panels have laterally, at either end, a guide edge to slide vertically within panel guide of the rail post. For deep excavation, the rail post may have one or more intermediate members sliding between the outer member and the inner member. Similarly to the outer member and the inner member of the rail post, the intermediate member has laterally, on either side, a panel guide and is provided with a front guide and a back guide to interlock respectively with the inner member and the outer member of the rail post.
There are many devices used to shore the walls of open excavations. Such shoring devices are commonly called trench or manhole shields. The trench shields have usually two panels held by individual spreaders pinned or bolted onto the extremities of each panel via flanges or fixed connectors. The manhole shields have four panels forming together a solid box. These devices are rigid in a sense that they do not allow relative movement between spreaders and panels and are usually installed after excavation is completed.
Another type of shoring device, which is commonly called slide rail shoring system, uses rail posts spreader systems and large shoring panels. The shoring system has a plurality of pairs of opposite rail posts spaced along the trench in the way that each pair is supported by a spreader frame, which slides in between the rail posts. Each rail support is provided on either side with guide channels where edges of large shoring panels slide within so that every two adjacent rails are connected with at least one shoring panel. This type of shoring device is currently used in the construction projects and depending on each specific design provides a wide range of conflicting or arguable results.
U.S. Pat. Nos. 3,910,053 and 4,657,442 (Krings), U.S. Pat. Nos. 5,310,289 and 5,503,504 (Hess et al.), U.S. Pat. No. 6,164,874 (May) disclose various slide rail shoring systems, all of them including multiple pairs of columns, spreader systems and large shoring panels. The support columns, or as well called as the rail posts, are made in one piece for the entire depth of the excavation or shoring wall. As result, various issues must be overcome when using current slide rail shoring systems. First of all, when assembling the shoring system the rail posts are vertically away up in the air, often conflicting with overhead obstacles such as electric lines, trees and can not be installed in highway underpasses, under bridges or overpasses, inside building, etc. In addition, the shoring panel accesses the guide of the rail post from the upper end rendering the installation very difficult, often time consuming and dangerous for the workers. Also, when pushing the rail posts or the entire shoring system down as excavation deepens, the upper or previously installed shoring panels are in permanent friction with the rail posts increasing drastically the resistive forces. As result, the rail posts often rotate or lean out of aplomb binding the entire shoring system. When this happen, the entire shoring system has to be to removed and reinstalled. Other issues such as the weight of rail posts, their damages and especially the difficulties during the removal have limited the use and increased the cost of slide rail shoring system. Yet another critical issue, is the limited depth of excavation due to above mentioned reasons as well as the fact that many panels must be staked what creates insurmountable difficulties during removal of the shoring system. The slide rail shoring system is a dig and push system by mean that is installed simultaneously to the excavation only, never afterward. Or, in hard soils, it becomes very difficult to push down each component of these shoring systems and it's necessary to dig underneath the rail posts and shoring panels what is not always possible or accessible.
Other knowing shoring device that has panels sliding vertically within excavation without using vertical support columns is disclosed in U.S. Pat. No. 6,224,296 (Fukumori). This device uses two pairs of large shoring panels. The first pair of panels, which shores the upper part of trench pressing against the excavation walls, is fixed at ground level. The second pair of panels slides within first pair shoring thereby the lower part of excavation. Both pairs of panels are connected and use sets of rigging to control the installation and removal of this device. Such device performs poorly in deep excavation and requires accurate installation regarding the space between first pair of panels their parallelism, etc. The removal of the panel is also associated with damages of guiding pair of panels.